Currently, the market for liquid-crystal displays and plasma displays has been growing, and accordingly, demand for transparent conductive films that are essential for such displays has been increasing. The transparent conductive films are applied to, other than such displays, touch panels, solar cells, antistatic materials, electromagnetic shielding materials, sheet heating elements, and so on. Indium Tin Oxide (ITO) is widely applied as the transparent conductive film. However, since Indium is expensive and exhaustion of resources is a concern, there have been examined transparent conductive films that can substitute for the ITO. The transparent conductive films that can substitute for the ITO include, as candidates, carbon nanotube (hereinafter, referred to as CNT) films, zinc oxide (hereinafter, referred to as ZnO), and so on. The CNT especially has a feature that the CNT is applicable to a flexible film, to which the ITO and the ZnO are difficult to be applied.
The CNT film can be obtained by applying a dispersion liquid, in which the CNT is dispersed, onto a base material and drying the same liquid, by using a dip coating method, a spin coating method, a spray coating method, and the like. In order to obtain a CNT film having excellent properties by using such methods, it is necessary to prepare a dispersion liquid, in which the CNT is stably dispersed.
As a method for dispersing the CNT into a dispersion medium, there have been suggested a method in which the CNT is treated by acid (Non-Patent Document 1), a method in which the CNT is treated by plasma (Patent Document 1), a method in which a surface acting agent is added (Patent Document 2), or the like.